1. Field of the Invention
The present invention relates to heat recovery systems, and in particular relates to such systems which recover the waste heat of air conditioning and refrigeration systems for purposes of heating water.
2. Description of the Prior Art
Because of the rapidly rising costs of energy, the incentives to conserve energy are increasing, both for industrial users and domestic users. Consequently there is considerable interest in not only eliminating energy waste by making equipment more efficient, but also by recovering energy such as waste heat which, according to conventional practice, is usually injected into the atmosphere without recovery.
It is well known in the art to use some of the heat from the condensing process of a refrigeration system to produce hot water in a storage tank. Heat is reclaimed by employing a heat exchanger in the hot gas line between the compressor and the condenser of the air conditioning system. Water from the bottom of the hot water heater is circulated through the heat exchanger by means of a small circulating pump. This basic arrangement has been used with success and is gaining widespread acceptance; but there is continuing interest in improving this basic system to make it more efficient and responsive.
The potential for energy conservation by the recovery of waste heat in the home and in industrial applications is substantial because of the amount of energy required to operate air conditioning equipment and hot water heating equipment, both of which are significant users of energy. For example, an air conditioning system with a water cooled condenser, while producing a ton of refrigeration or 12,000 BTUH of cooling capacity, also produces approximately 15,000 BTUH of heat which is rejected to the atmosphere. An air conditioning system with an air cooled condenser rejects about 16,000 to 17,000 BTUH for each ton or 12,000 BTUH of cooling capacity. Of this 15,000 to 17,000 BTUH of heat for each ton of capacity, 3,000 to 5,000 BTUH is relatively easy to recover at a very nominal expense. Generally, the refrigeration system is operated totally separate from the hot water system with the result that the heat removed from the condensing process is wasted, while the water in the hot water system is heated by means of an auxiliary energy source such as gas, electricity, or oil. The cost of such fuel and energy can be great particularly in situations where a large amount of hot water is required.
One problem associated with the installation of a hot gas-to-water heat exchanger for recovery of waste heat in an existing refrigeration or air conditioning system is that the hot gas refrigerant line from the compressor to the condenser must be cut to connect the refrigerant passage of the heat exchanger. During this procedure, the refrigerant charge is lost to the atmosphere and requires that the entire refrigerant system be purged, evacuated and recharged with refrigerant. An additional problem is that of replacing the heat exchanger from time to time because of malfunction or maintenance, or for substituting a larger or smaller heat exchanger as hot water production requirements change. Because of the very large amount of waste heat which can be recovered from the refrigeration process, it may be desirable to substitute a more efficient or a larger capacity heat exchanger in place of a relatively smaller one to satisfy increased hot water production requirements. This substitution procedure cannot be carried out in conventional heat recovery systems without severing the refrigerant line leading to the heat exchanger which requires that the system be purged, evacuated and recharged with refrigerant which is both time consuming and expensive. Additionally, it may be desirable to temporarily thermally decouple the heat exchanger from the refrigeration system when the hot water system is undergoing maintenance or has been withdrawn from service, and later re-establish the heat transfer relation when hot water service has been restored. Such an arrangement which would permit thermal decoupling without requiring mechanical detachment of the heat exchanger would provide a substantial saving of time and labor.